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Spacecraft and Instrument

Image above: Kepler's Earth Trailing Orbit Around the Earth. Credit: NASA An Earth-trailing heliocentric orbit with a period of 372.5 days provides the optimum approach to meeting of the scientific objectives. In this orbit the spacecraft slowly drifts away from the Earth and is at a distance of 0.5 Astronomical Unit (AU) (worst case) at the end of four years.

Another advantage of this orbit is that it has a very-low disturbing torque on the spacecraft, which leads to a very stable pointing attitude. Not being in Earth orbit means that there are no torques due to gravity gradients, magnetic moments or atmospheric drag. The "largest" external torque then is that caused by solar pressure. This orbit also avoids the high radiation dosage associated with an Earth orbit, but from time to time is subject to solar flares. Telecommunications and navigation for the mission are provided by NASA's Deep Space Network (DSN).

Mission Duration

The mission must last long enough to detect and confirm the periodic nature of the transits of planets in or near the Habitable Zone. A three and one-half or more year mission is currently envisioned which enables a four-transit detection of most orbits up to one year in length and a three-transit detection of orbital periods up to 1.75 years.